A received signal strength indicator (RSSI) provides information regarding the received power level of a radio frequency (RF) signal at a wireless device (e.g., a cellular phone, a wireless phone, a wireless network card, etc.) Based on the RSSI, the wireless device can then determine whether to continue or terminate operation and can adjust amplifier gains and/or frequency bandwidth of various internal components.
FIG. 1 is a schematic diagram illustrating a rectifier 10 for measuring RSSI in accordance with the prior art. As shown in FIG. 1, the rectifier 10 includes a capacitor 14 coupled to a bias resistor 16, a diode 18, and a low pass filter 20. The capacitor 14, the diode 18, and the low pass filter 20 together convert the received radio frequency signal 12 into a low frequency signal. The envelope power level of the low frequency signal then provides the measured RSSI 22.
The measurement of RSSI, however, can be susceptible to environmental and/or process influence. Operating temperatures, inherent silicon mismatch of internal components, and/or other factors may cause the measured RSSI to be inaccurate. For example, the measured RSSI may falsely indicate insufficient signal levels even when the received signal has sufficient strength. Such inaccuracy may cause the wireless device to malfunction.
A conventional technique for addressing the inaccuracy includes trimming the rectifier with resistors by, e.g., adjusting the resistance of the bias resistor 16. However, trimming with resistors is laborious and costly because different resistors must be individually formed or attached to each chip. Trimming with resistors can also be inefficient because the trimming only affects the measured RSSI at a particular operating state. As a result, an efficient technique for addressing the inaccuracy in RSSI measurement is desired.